Process for the production of H2 O2 from the elements

ABSTRACT

The present invention concerns a process for the production of hydrogen peroxide by reacting a gas mixture which contains hydrogen and oxygen in an aqueous reaction medium containing less than 2% by volume liquid organic components and in the presence of a metallic catalyst which is characterized in that a palladium/gold alloy with 5 to 95 atom percent gold or a palladium/iridium or palladium/rhodium bimetal with 1 to 15 atom percent iridium or rhodium is used as the catalyst.

This application is a continuation of application Ser. No. 08/108,581filed Nov. 17, 1993 now abandoned.

DESCRIPTION

The invention concerns a process for the production of hydrogen peroxideby reacting hydrogen and oxygen in aqueous suspension in the presence ofa catalyst.

Hydrogen peroxide is used in large amounts in industry e.g. to bleachwood, textiles, paper, oils, fats, to produce bleaching agents for thedetergent industry and in particular sodium perborate, and for cleansingagents and cosmetics, to bleach hair, as starting product for epoxides,peroxide catalysts, glycerol, plasticizers, alkyl and acyl peroxide,peroxocarboxylic acids, for disinfection and to an increasing extent inthe field of environmental protection to detoxify and deodorize water,waste water and waste air, to bleach pulp, deink waste papter, todesulphurize flue gas, to clean Si chips in the electronic industry etc.

Since it can be used in a great variety of ways and is important inindustry, the production processes for hydrogen peroxide is thereforebecoming increasingly important. The usual industrial processes for theproduction of hydrogen peroxide are based on oxidation processes usingisopropanol and on autoxidation processes using anthraquinones.

Various methods for the direct synthesis of hydrogen peroxide fromhydrogen and oxygen have also already been proposed.

EP-B 0 049 806 describes a process for the direct synthesis of hydrogenperoxide using a palladium supported catalyst in a liquid medium whichis comprised of methanol and contains up to 1% by weight formaldehyde.

According to EP-B 0 117 306 an acidic aqueous solution which contains anoxygen-containing organic compound is used in the presence of apalladium catalyst.

A process for the direct synthesis from hydrogen and oxygen is knownfrom U.S. Pat. No. 4,336,239 which is carried out in an acidic aqueoussolution containing methanol or acetone in the presence of a supportedcatalyst with a platinum metal e.g. palladium as the catalyticallyactive metal.

A process is known from EP-B 0 049 809 for the direct synthesis ofhydrogen peroxide by contacting a gas mixture containing hydrogen andoxygen with an acidic aqueous liquid which contains up to 95% by volumeof a ketone, aldehyde or alcohol in which the formation of hydrogenperoxide takes place on a supported catalyst and detached palladiumsalts are removed for example by an ion exchange resin in order toprolong the effective life-span of the catalyst and to inhibit thedecomposition of the hydrogen peroxide formed.

A disadvantage of the aforementioned processes is the use of organicsubstances as a component of the liquid reaction medium.

When organic substances are present this is associated with thepossibility that organic peroxides may be formed which can lead to ahigh inflammability of the solvents used and the formation of explosivemixtures with hydrogen peroxide (cf. e.g. Schumb et al., HydrogenPeroxide, Reinhold Publishing Corporation, 179 (1955); Swern, OrganicPeroxides, Wiley--Interscience New York, 26 (1970)2). By this means thepossibility of danger considerably increases when direct syntheses arecarried out in this manner.

With regard to carrying out the procedure more safely and thepurification of the hydrogen peroxide which formed it is moreadvantageous to carry out the direct synthesis from hydrogen and oxygenin an aqueous medium which is as free as possible of organic components.

Such a process is described in EP-A 0 132 294 in which a commerciallyavailable or in situ generated palladium supported catalyst is used inan aqueous reaction medium which is essentially free of organiccomponents and in which the hydrogen ion and chloride ion concentrationis between 0.01 and 2 mol/l. The reaction is carried out at a totalpressure of up to 100 bar.

A similar process is known from EP-A 0 274 830 in which the aqueousreaction medium contains sodium bromide and sulphuric acid whereby theuse of bromide ions yields better results compared to the use ofchloride ions at the same concentration with regard to selectivity andyield. Supported catalysts which are coated with palladium/platinumbimetals can also be used instead of palladium supported catalysts (cf.EP-A 0 342 048).

A process for the production of hydrogen peroxide is known from U.S.Pat. No. 4,393,038 in which hydrogen is passed through apalladium-containing membrane into an aqueous solution which containsstabilizing ions in addition to dissolved oxygen; a gold/palladium tubeis for example used as the palladium-containing membrane.

DE-B 26 55 920 describes a process for the production of hydrogenperoxide by reacting hydrogen with oxygen in the presence of a catalystfrom the platinum group, which must contain a certain amount of adsorbedhydrogen, in an aqueous medium in the presence of hydrochloric acid andphosphoric acid. Alloys or mixtures of the platinum metals with othermetals such as gold are also mentioned as catalysts. However, only theuse of a palladium-silicic acid catalyst is disclosed. The catalyst isused in a colloidal form or on a support and a hydrogen peroxideconcentration of 8 to 11% by weight is maintained in the outflow.

EP-A 0 366 419 discloses a process for the production of hydrogenperoxide by reacting hydrogen and oxygen in an acidic aqueous medium. Inthis process at least one metal from group VIII on a hydrophobic supportis used as the catalyst, wherein Pt, Pd, Ru, Rh and Ir are preferred.However, only the use of a platinum-carbon catalyst is disclosed. Inaddition the reaction medium contains 0.03 mol/l halogenide ions.

EP-A 0 415 448 discloses a process for the production of hydrogenperoxide by the catalytic reaction of hydrogen with oxygen in a liquidaqueous reaction medium in which metals of the Pt group, in particularplatinum and palladium, are either used alone or on a solid support.Palladium-active charcoal and colloidal palladium are disclosed as thecatalysts.

Although the use of an aqueous medium which contains no organiccomponents can avoid problems associated with the use of organiccomponents, the use of the above-mentioned aqueous systems withpalladium or platinum catalysts and with a relatively high content ofacids or/and halogenides is also not satisfactory with regard to theapparative requirements, the attendant environmental pollution and inparticular also with regard to their effect of decreasing the stabilityof the hydrogen peroxide formed.

The object of the present invention is therefore to provide a processfor the production of hydrogen peroxide by the direct reaction ofhydrogen and oxygen in which the aforementioned disadvantages can beavoided to a large extent and which can be carried out easily and with ahigh degree of safety.

In particular it is intended to provide a process for the production ofhydrogen peroxide from the elements with which it is possible toincrease the rate of formation, selectivity or/and yield of hydrogenperoxide compared to methods of the state of the art.

The object according to the present invention is achieved by a processfor the production of hydrogen peroxide by reacting a gas mixture whichcontains hydrogen and oxygen in an aqueous reaction medium containingless than 2% by volume liquid organic components and in the presence ofa metallic catalyst which is characterized in that a palladium/goldalloy with 5 to 95 atom percent gold or a palladium/iridium orpalladium/rhodium bimetal with 1 to 15 atom percent iridium or rhodiumis used as the catalyst.

The aqueous reaction medium contains less than 2% by volume, preferablyless than 0.5% by volume liquid organic components. It is particularlypreferred that the reaction medium is completely free of organiccomponents.

The reaction medium preferably contains less than 0.01 mol/l halogenideions, particularly preferably 0.000001 mol/l to 0.01 mol/l halogenideions and most preferably between 0.00001 mol/l and 0.001 mol/lhalogenide ions. The halogenide ions are preferably bromide or/andchloride ions and particularly preferably bromide ions.

The gas mixture used in the process according to the present inventionpreferably contains no more than 20% by volume hydrogen. Furthermore thereaction is preferably carried out at an increased pressure,particularly preferably at a total pressure of at least 10 bar and mostpreferably at a total pressure of 40 to 200 bar.

The reaction temperature is generally between 0° and 100° C. andpreferably between 15° and 70° C. Furthermore the reaction medium shouldpreferably contain up to 2 mol/l, particularly preferably 0.001 mol/l to0.5 mol/l of an acid which should preferably not be a hydrohalic acid.This acid is preferably a strong inorganic acid for example sulphuricacid or/and phosphoric acid.

If a palladium/iridium or palladium/rhodium bimetal is used as thecatalyst then the content of iridium or rhodium is preferably 3 to 10atom %. If on the other hand a palladium/gold alloy is used as thecatalyst the gold content is preferably 5 to 80 atom %, particularlypreferably 10 to 50 atom % and most preferably 20 to 50 atom %.

The catalyst can be present in the form of a finely dispersed metalpowder as well as bound to a solid supporting material. A catalyst inthe form of finely dispersed metal powder is preferably produced byreducing a palladium halogenide and a gold, iridium or rhodiumhalogenide in the desired ratios to one another in an aqueous solutionusing a suitable reducing agent, in particular sodium borohydride, andsubsequently removing the halogenide ions from the aqueous solution.

If a catalyst is used that is present bound to a solid supportingmaterial then the proportion of catalytically active metal is preferably0.1 to 10% by weight particularly preferably 0.5 to 5% by weight andmost preferably 1 to 3% by weight relative to the total weight of metaland supporting material. The supporting material is preferably ahydrophilic material which is selected from the group comprising activecharcoal, materials based on silicic acid (e.g. silica gel, hydroussilicic acid), silicon carbide, zeolites, titanium dioxide, zirconiumdioxide and aluminium oxide. Aluminium oxide is particularly preferablyused as the supporting material. The production of the catalyst bound toa support is preferably carried out by reduction of a palladiumhalogenide and of a gold, iridium or rhodium halogenide in the desiredratio to one another in aqueous solution and in the presence of theappropriate amounts of supporting material using a reducing agent, inparticular a formate, and subsequently removing the halogenide ions fromthe solution.

A preferred catalyst within the scope of the invention consists of apalladium-gold alloy with a content of 10 to 30 atom % gold on analuminium oxide support. The amount of alloy is preferably 0.5 to 5,particularly preferably 0.1 to 3% by weight in relation to the totalweight of the catalyst.

A particularly suitable catalyst for the present invention can beproduced by mixing a hydrochloric acid solution of palladium chlorideand gold chloride in the desired ratio of palladium:gold with thecorresponding amount of supporting material, preferably aluminium oxide,at a weakly acidic pH value, advantageously between pH 5 and 6.5,heating, adding a reducing agent, in particular a formate, in excess andremoving the chloride ions after the reduction is completed. It isexpedient to carry out the heating at a weakly acidic pH value attemperatures between 50° and 90° C.; the reduction is likewise carriedout at an increased temperature up to the boiling temperature.

Surprisingly by using the catalysts according to the present invention,an increase in the rate of formation, selectivity or/and yield ofhydrogen peroxide can be achieved compared to the usual palladiumcatalysts.

The process according to the present invention can be carried outsemi-continuously e.g. in a stirred autoclave which contains the liquidaqueous reaction medium whereby the gas mixture containing oxygen andhydrogen is passed through while stirring. In this process thetemperature, pressure and flow-rate of the gases are monitoredaccordingly and adjusted accordingly. The process according to thepresent invention can also be carried out in a continuous manner usingappropriate equipment.

The following examples serve to further elucidate the present invention.

EXAMPLES 1 to 11

8.4 mg of a commercially available palladium/gold supported catalystwhich is coated with 5% by weight total metal on active charcoal Da 32/4(Heraeus GmbH) was fed into a 500 ml stirred autoclave lined with Teflonand suspended in 115 g 0.05 molar sulphuric acid which contained0.000068 mol/l sodium bromide.

The autoclave was closed and pressurized with 10 bar oxygen. The oxygenwas subsequently discharged. This procedure was repeated twice in orderto remove residual nitrogen from the autoclave. Afterwards 80 bar oxygenwas applied and the temperature was held constant at 25° C. After thetarget temperature had been reached, 0.177 Nl/min oxygen and 0.0345Nl/min hydrogen were passed through while stirring. The total pressureof 80 bar was kept constant using a pressure regulator. The reactiontime was 177 min.

The amount of hydrogen consumed per hour and gram palladium and theselectivity were determined by the increase in weight after completionof the reaction and the amount of hydrogen peroxide formed wasdetermined by titration with a 0.1 n cerium sulfate solution.

The amount of converted hydrogen was calculated as follows:

Mass H₂ O₂ =titrated mole H₂ O₂ ×34

mole H₂ O=(increase in weight--mass H₂ O₂)/18

converted mole H₂ =mole H₂ O₂ --mole H₂ O

converted mole H₂ /(hxgPa)=converted mole H₂ ×60 (reaction time xgPd)

The selectivity was calculated as follows:

S=titrated mole H₂ O₂ /reacted mole H₂

                  TABLE 1                                                         ______________________________________                                        Ex-              Converted mole                                                                            Bound mole                                                                              Selec-                                 ample Catalyst   H.sub.2 (hxgPd)                                                                           H.sub.2 O.sub.2 /(hxgPd)                                                                tivity                                 No.   % Pd/% Au  mole/(hxgPd)                                                                              mole/(hxgPd)                                                                            %                                      ______________________________________                                        1     5/--       32.4        20.8      64                                     2     4.5/0.5    36.0        22.7      63                                     3     4.25/0.75  31.6        17.7      56                                     4     4.0/1.0    37.4        24.0      64                                     5     3.5/1.5    51.7        33.1      64                                     6     3.0/2.0    48.3        30.9      64                                     7     2.5/2.5    81.5        49.7      61                                     8     2.0/3.0    61.4        32.6      53                                     9     1.0/4.0    99.7        47.8      48                                     10    0.5/4.5    73.9        29.5      40                                     11    --/5.0     0           0         --                                     ______________________________________                                    

EXAMPLES 12 to 16

The reaction was carried out as described in examples 1 to 11. However,the total pressure was lowered to 60 bar and the reaction time wasdecreased to 159 min.

                  TABLE 2                                                         ______________________________________                                        Ex-              Converted mole                                                                            Bound mole                                                                              Selec-                                 ample Catalyst   H.sub.2 (hxgPd)                                                                           H.sub.2 O.sub.2 /(hxgPd)                                                                tivity                                 No.   % Pd/% Au  mole/(hxgPd)                                                                              mole/(hxgPd)                                                                            %                                      ______________________________________                                        12    5.0/--     36.4        26.9      74                                     13    4.25/0.75  41.5        29.0      70                                     14    3.5/1.5    40.5        30.3      75                                     15    2.5/2.5    51.9        38.9      75                                     16    1.0/4.0    136.2       99.5      73                                     ______________________________________                                    

EXAMPLES 17 to 20

The reaction was carried out as described in examples 1 to 11 exceptthat the total pressure was 40 bar and the reaction time was 159 min.

                  TABLE 3                                                         ______________________________________                                        Ex-              Converted mole                                                                            Bound mole                                                                              Selec-                                 ample Catalyst   H.sub.2 (hxgPd)                                                                           H.sub.2 O.sub.2 /(hxgPd)                                                                tivity                                 No.   % Pd/% Au  mole/(hxgPd)                                                                              mole/(hxgPd)                                                                            %                                      ______________________________________                                        17    4.25/0.75  28.2        19.7      70                                     18    3.5/1.5    32.6        23.8      73                                     19    2.5/2.5    58.4        40.9      70                                     20    1.0/4.0    110.4       77.3      70                                     ______________________________________                                    

EXAMPLES 21 to 25

The reaction was carried out as described in examples to 11 except thatthe temperature was 10° C., 17.5 mg catalyst was added and the reactiontime was increased to 248 min.

                  TABLE 4                                                         ______________________________________                                        Ex-              Converted mole                                                                            Bound mole                                                                              Selec-                                 ample Catalyst   H.sub.2 (hxgPd)                                                                           H.sub.2 O.sub.2 /(hxgPd)                                                                tivity                                 No.   % Pd/% Au  mole/(hxgPd)                                                                              mole/(hxgPd)                                                                            %                                      ______________________________________                                        21    5.0/--     22.2        15.5      70                                     22    4.25/0.75  25.4        17.9      70                                     23    3.5/1.5    25.9        18.9      73                                     24    2.5/2.5    42.2        27.4      64                                     25    1.0/4.0    73.7        47.2      64                                     ______________________________________                                    

EXAMPLES 26 to 30

The reaction was carried out as described in examples 21 to 25 exceptthat the sodium bromide concentration was 0.000165 mol/l.

                  TABLE 5                                                         ______________________________________                                        Ex-              Converted mole                                                                            Bound mole                                                                              Selec-                                 ample Catalyst   H.sub.2 (hxgPd)                                                                           H.sub.2 O.sub.2 /(hxgPd)                                                                tivity                                 No.   % Pd/% Au  mole/(hxgPd)                                                                              mole/(hxgPd)                                                                            %                                      ______________________________________                                        26    5.0/--     22.1        14.8      67                                     27    4.25/0.75  34.5        21.0      61                                     28    3.5/1.5    30.9        19.7      64                                     29    2.5/2.5    32.9        21.4      65                                     30    1.0/4.0    79.1        49.8      63                                     ______________________________________                                    

EXAMPLES 31 to 38

40 mg palladium/gold-supported catalyst was fed into a 300 ml stirredautoclave and suspended in 40 ml 1.6 molar phosphoric acid whichcontained 0.0006 mol/l sodium bromide. The stirred liquid reactionmixture was held at a temperature of 25° C. and a gas mixture streamcontaining 4.5% hydrogen and 95.5% oxygen was passed through. The gasflow was 100 Nl/h, the pressure was 80 bar and the reaction time 120min. The experiments were evaluated analogously to examples 1-30 viatitration of hydrogen peroxide and increase in weight at the end of thereaction.

                  TABLE 6                                                         ______________________________________                                        Ex-              Converted mole                                                                            Bound mole                                                                              Selec-                                 ample Catalyst   H.sub.2 (hxgPd)                                                                           H.sub.2 O.sub.2 /(hxgPd)                                                                tivity                                 No.   % Pd/% Au  mole/(hxgPd)                                                                              mole/(hxgPd)                                                                            %                                      ______________________________________                                        31    5/--       22.5        14.2      63                                     32    4.5/0.5    22.2        15.6      70                                     33    4.25/0.75  22.4        15.6      70                                     34    4.0/1.0    24.4        17.0      70                                     35    3.5/1.5    27.1        19.5      72                                     36    3.0/2.0    29.2        20.7      71                                     37    2.5/2.5    31.0        21.7      70                                     38    2.0/3.0    30.0        19.2      64                                     ______________________________________                                    

EXAMPLES 39 to 42

A) Process for the production of the catalysts

The catalyst used was a preparation obtained by applying a 2% by weightalloy consisting of palladium and gold onto a support of aluminiumoxide.

The catalyst was produced in the following manner: A fine powder ofaluminium oxide was added to a solution which had been obtained bydissolving a certain amount palladium chloride and gold chloride inaqueous 0.1N hydrochloric acid in such an amount that the total amountof metallic palladium and gold was 2% by weight in relation to aluminiumoxide and the ratios of palladium to gold were 50, 30 and 10 atom %gold. The suspension was stirred and the pH value was adjusted to 6 bymeans of 10% by weight sodium hydroxide solution and subsequently heatedto 80° C. An aqueous sodium formate solution which was prepared from 15g sodium formate and 85 g deionized water was added to this solution insuch an amount that the molar ratio of sodium formate to palladium was40. The suspension was heated to boiling and 5 min after completion ofthe reduction it was slowly cooled. The catalyst was filtered off,washed with deionized water until free of chloride and dried for 10hours in a vacuum at 100° C.

B) H₂ O₂ synthesis

40 mg of a palladium/gold supported catalyst obtained according to A)which is coated with 2% by weight total metal on aluminium oxide wasadded to a 500 ml stirred autoclave lined with Teflon and suspended in160 g 0.05 molar sulphuric acid which contained 0.00003 mol/l sodiumbromide.

The autoclave was closed and pressurized with 10 bar oxygen. The oxygenwas subsequently discharged. This procedure was repeated twice in orderto remove residual nitrogen from the autoclave. Afterwards 80 bar oxygenwas applied and the temperature was held constant at 25° C. As soon asthe target temperature had been reached, 0.168 Nl/min oxygen and 0.03365Nl/min hydrogen were passed through while stirring. The total pressureof 80 bar was kept constant using a pressure regulator. The reactiontime was 600 min.

                  TABLE 7                                                         ______________________________________                                        Ex-   Catalyst   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % Pd/   H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   at % Au    mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        39    100/--     28.9        11.9      41                                     40    90/10      42.9        16.7      39                                     41    70/30      77.8        35.8      46                                     42    50/50      117.5       50.5      43                                     ______________________________________                                    

EXAMPLES 413 to 44

The reaction was carried out as described in examples 39 to 42, however,the total pressure was lowered to 40 bar.

                  TABLE 8                                                         ______________________________________                                        Ex-   Catalyst   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % Pd/   H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   at % Au    mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        43    100/--     26.3        9.7       37                                     44    50/50      89.3        26.8      30                                     ______________________________________                                    

EXAMPLES 45 to 46

The reaction was carried out as described in examples 39 to 42, however,the total pressure was lowered to 20 bar.

                  TABLE 9                                                         ______________________________________                                        Ex-   Catalyst   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % Pd/   H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   at % Au    mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        45    100/--     15.5        5.6       36                                     46    50/50      63.1        19.6      31                                     ______________________________________                                    

EXAMPLES 47 to 48

The reaction was carried out as described in examples to 4, however, thehydrogen stream was lowered to 0.02356 Nl/h.

                  TABLE 10                                                        ______________________________________                                        Ex-   Catalyst   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % Pd/   H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   at % Au    mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        47    100/--     22.4        10.8      48                                     48    90/10      83.0        26.8      40                                     ______________________________________                                    

EXAMPLES 49 to 50

The reaction was carried out as described in examples 1 to 4, however,the hydrogen stream was lowered to 0.01346 Nl/h.

                  TABLE 11                                                        ______________________________________                                        Ex-   Catalyst   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % Pd/   H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   at % Au    mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        49    100/--     16.3        8.2       50                                     50    90/10      47.7        23.4      49                                     ______________________________________                                    

EXAMPLE 51

Production of a palladium/iridium catalyst bound to a support.

A fine powder of aluminium oxide was added to a solution which had beenobtained by dissolving palladium chloride and iridium chloride inaqueous 0.1N hydrochloric acid so that the total amount of metallicpalladium and iridium was 2% by weight relative to aluminium oxide andthe ratio of palladium to iridium was between 3 and 10 atom % iridium.The suspension was stirred, the pH adjusted to 6 with 10% by weightsodium hydroxide solution and subsequently heated to 80° C. An aqueoussodium formate solution which was prepared from 15 g sodium formate and85 g deionized water was added to this solution in such an amount thatthe molar ratio of sodium formate to palladium was 40:1. The suspensionwas heated to boiling and 5 minutes after completion of the reduction itwas slowly cooled. The catalyst was filtered off, washed with deionizedwater until free of chloride and dried for 10 hours in a vacuum at 100°C.

EXAMPLE 52

Production of palladium/gold, palladium/iridium, palladium/rhodiumcatalysts in a finely dispersed form.

Precipitates obtained by common reduction of their chlorides from thesolution were used as catalysts. The catalyst was prepared in thefollowing manner. The chlorides of the metals to be reduced were mixedin the amounts that corresponded to the composition of the catalyst tobe prepared. The mixed salts were dissolved in ca. 50 ml ca. 1 mol/lhydrochloric acid per g catalyst and added dropwise at a rate of 1ml/sec into 66 ml of an aqueous reduction solution per g catalyst thatwas heated to 80° C. and stirred and which contained 8% by weight sodiumhydroxide and 5% by weight sodium borohydride. The reduction was carriedout in a suitable glass apparatus consisting of a round-bottom flaskwith an attached reflux condenser, thermometer, stirring apparatus anddropping funnel. The preparations obtained in this manner were filtered,washed to neutrality with deionized water and dried in a vacuum at 100°C. The dried preparations were subsequently subjected to a hydrogenstream of 1 Nm³ /h for 1 h at 240° C.

EXAMPLES 53 to 56

40 mg of a palladium/iridium bimetal supported catalyst which was coatedwith 2% by weight total metal on aluminium oxide and prepared accordingto example 51 was fed into a 500 ml stirred autoclave lined with Teflonand suspended in 150 g 0.05 M sulphuric acid which contained 0.00003mol/l sodium bromide.

The autoclave was closed and pressurized with 10 bar oxygen. The oxygenwas subsequently discharged. This procedure was repeated twice in orderto remove residual nitrogen from the autoclave. Afterwards 80 bar oxygenwas applied and the temperature was held constant at 25° C. After thetarget temperature had been reached, 0.168 Nl/min oxygen and 0.03365Nl/min hydrogen were passed through while stirring. The total pressureof 80 bar was kept constant using a pressure regulator. The reactiontime was 600 min.

The amount of hydrogen consumed per hour and gram palladium (H₂/(h*gPd)) and the selectivity were determined by the increase in weightafter completion of the reaction and the amount of hydrogen peroxideformed per hour and gram palladium (H₂ /(h*gPd)) was determined bytitration with a 0.1 n cerium sulfate solution.

The amount of converted hydrogen was calculated as follows:

Mass H₂ O₂ =titrated mole H₂ O₂ * 34

mole H₂ O=(increase in weight--mass H₂ O₂)/18

converted mole H₂ =mole H₂ O₂ --mole H₂ O

converted mole H₂ /(h*gPd)=converted mole H₂ +60/(reaction time *gPd)

The selectivity was calculated as follows:

S=titrated mole H₂ O₂ /converted mole H₂

                  TABLE 12                                                        ______________________________________                                        Ex-   Catalyst   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % Pd/   H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   at % Ir    mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        53    100/--     28.9        11.9      41                                     54    95/5       44.8        22.0      49                                     55    92.3/7.7   62.7        25.1      40                                     56    0/100      0           0         --                                     ______________________________________                                    

EXAMPLES 57 to 58

The reaction was carried out analogous to the process described inexamples 53 to 56, however, the total pressure in the autoclave waslowered to 40 bar.

                  TABLE 13                                                        ______________________________________                                        Ex-   Catalyst   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % Pd/   H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   at % Ir    mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        57    100/--     26.3        9.7       37                                     58    92.3/7.7   45.8        17.9      39                                     ______________________________________                                    

EXAMPLES 59 to 60

The reaction was carried out analogous to the process described inexamples 53 to 56, however, the total pressure in the autoclave waslowered to 20 bar.

                  TABLE 14                                                        ______________________________________                                        Ex-   Catalyst   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % Pd/   H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   at % Ir    mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        59    100/--     15.5        5.6       36                                     60    92.3/7.7   33.5        10.7      32                                     ______________________________________                                    

EXAMPLES 61 to 62

The reaction was carried out analogous to the process described inexamples 53 to 56, however, the hydrogen stream was lowered to 0.02356Nl/h.

                  TABLE 15                                                        ______________________________________                                        Ex-   Catalyst   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % Pd/   H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   at % Ir    mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        61    100/--     22.4        10.8      48                                     62    92.3/7.7   34.8        17.1      49                                     ______________________________________                                    

EXAMPLES 63 to 64

The reaction was carried out analogous to the process as described inexamples 53 to 56, however, the hydrogen stream was lowered to 0.01346Nl/h.

                  TABLE 16                                                        ______________________________________                                        Ex-   Catalyst   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % Pd/   H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   at % Ir    mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        63    100/--     16.3        8.2       50                                     64    92.3/7.7   21.3        10.2      48                                     ______________________________________                                    

EXAMPLES 65 to 77

100 mg of a palladium/gold, palladium/iridium or palladium/rhodiumcatalyst prepared according to example 52 was fed into a 500 ml stirredautoclave lined with Teflon and suspended in 160 g 0.05 M sulphuric acidwhich contained 0.001 mol/l sodium bromide.

The autoclave was closed and pressurized with 10 bar oxygen. The oxygenwas subsequently discharged. This procedure was repeated twice in orderto remove residual nitrogen from the autoclave. Afterwards 40 bar oxygenwas applied and the temperature was held constant at 25° C. After thetarget temperature had been reached, 0.168 Nl/min oxygen and 0.01346Nl/min hydrogen were passed through while stirring. The total pressureof 40 bar was kept constant using a pressure regulator. The reactiontime was 177 min.

The amount of hydrogen consumed per hour and gram palladium, theselectivity and the amount of hydrogen peroxide formed per hour and grampalladium were determined as in example 53.

                  TABLE 17                                                        ______________________________________                                              Catalyst                                                                Ex-   at % Pd/   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % (Rh,  H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   Ir or Au)  mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        65    100/--     0.130       0.048     37                                     66    --/100 Rh  0           0         --                                     67    --/100 Ir  0           0         --                                     68    --/100 Au  0           0         --                                     69    95/5 Rh    0.124       0.055     45                                     70    90/10 Rh   0.247       0.099     40                                     71    95/5 Ir    0.169       0.106     63                                     72    90/10 Ir   0.261       0.071     27                                     73    95/5 Au    0.149       0.060     40                                     74    90/10 Au   0.175       0.077     44                                     75    80/20 Au   0.220       0.105     48                                     76    70/30 Au   0.288       0.153     53                                     77    50/50 Au   0.334       0.167     50                                     ______________________________________                                    

EXAMPLES 78 to 82

The reaction was carried out analogous to the process described inexamples 65 to 77 except that the amount of catalyst used was reduced to40 mg and the sodium bromide concentration was reduced to 0.000147mol/l.

                  TABLE 18                                                        ______________________________________                                              Catalyst                                                                Ex-   at % Pd/   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % (Rh,  H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   Ir or Au)  mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        78    100/--     0.178       0.071     40                                     79    95/5 Ir    0.289       0.191     66                                     80    90/10 Rh   0.493       0.281     57                                     81    90/10 Au   0.271       0.146     54                                     82    50/50 Au   0.557       0.306     55                                     ______________________________________                                    

EXAMPLES 83 to 87

The reaction was carried out analogous to the process described inexamples 65 to 77 except that the amount of catalyst used was reduced to40 mg and the sodium bromide concentration was reduced to 0.000027mol/l.

                  TABLE 19                                                        ______________________________________                                              Catalyst                                                                Ex-   at % Pd/   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % (Rh,  H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   Ir or Au)  mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        83    100/--     0.210       0.074     36                                     84    90/10 Rh   0.616       0.148     24                                     85    95/5 Au    0.243       0.134     55                                     86    90/10 Au   0.286       0.157     55                                     87    50/50 Au   0.581       0.308     53                                     ______________________________________                                    

EXAMPLES 88 to 91

The reaction was carried out analogous to the process described inexamples 65 to 77 except that the amount of catalyst used was 40 mg, thesodium bromide concentration was reduced to 0.000147 mol/l, the totalpressure was 60 bar and the reaction time was 10 hours.

                  TABLE 20                                                        ______________________________________                                              Catalyst                                                                Ex-   at % Pd/   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % (Rh,  H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   Ir or Au)  mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        88    100/--     0.361       0.135     37                                     89    95/5 Ir    0.545       0.262     48                                     90    90/10 Au   0.557       0.195     35                                     91    50/50 Au   1.173       0.422     36                                     ______________________________________                                    

EXAMPLES 92 to 96

The reaction was carried out analogous to the process described inexamples 65 to 77 except that the amount of catalyst used was 40 mg, thesodium bromide concentration was reduced to 0.000147 mol/l, the totalpressure was 80 bar and the reaction time was 10 hours.

                  TABLE 21                                                        ______________________________________                                              Catalyst                                                                Ex-   at % Pd/   Converted mole                                                                            Bound mole                                                                              Selec-                                 ample at % (Rh,  H.sub.2 (h*gPd)                                                                           H.sub.2 O.sub.2 /(h*gPd)                                                                tivity                                 No.   Ir or Au)  mole/(h*gPd)                                                                              mole/(h*gPd)                                                                            %                                      ______________________________________                                        92    100/--     0.507       0.187     37                                     93    95/5 Ir    0.639       0.269     42                                     94    90/10 Au   0.602       0.259     43                                     95    70/30 Au   1.053       0.400     38                                     96    50/50 Au   1.465       0.586     40                                     ______________________________________                                    

We claim:
 1. Process for the production of hydrogen peroxide comprising:forming a substantially nitrogen free gas mixture comprising hydrogen and oxygen; forming a substantially chloride free aqueous reaction mixture containing: less than 2% by volume liquid organic components, and sodium bromide in an amount sufficient to provide at least about 0.00001 mol per liter bromide ions and at most 0.01 mol per liter halogen ions; and mixing a halogenide of palladium with a halogenide of at least one member of the group consisting of iridium and rhodium to form a halogenide bimetal of palladium and 1 to 15 percent of at least one member selected from the group consisting of iridium and rhodium; reducing said mixture of a halogenide of palladium and a halogenide of at least one member selected from the group consisting of iridium and rhodium, with a non-hydrogen producing reducing agent consisting essentially of sodium formate to form a reduced bimetallic catalyst comprising palladium and 1 to 15 weight percent of at least one metal selected from the group consisting of iridium and rhodium; admixing said reduced bimetallic catalyst into said aqueous reaction mixture; passing said gas mixture through said aqueous reaction mixture; and contacting said gas mixture, in said aqueous reaction mixture, with said reduced bimetallic catalyst under conditions sufficient to convert hydrogen and oxygen in said gas mixture into hydrogen peroxide.
 2. Process as claimed in claim 1 wherein the reaction medium contains 0.00001 mol/l to 0.001 mol/l halogenide bromide ions.
 3. Process as claimed in claim 1, wherein said palladium/iridium or palladium/rhodium bimetal contain 3 to 10 atom percent iridium or rhodium respectively.
 4. Process as claimed in claim 1, wherein said palladium/gold alloy contains 10 to 50 atom percent gold.
 5. Process as claimed in claim 1, wherein said gas mixture contains up to 20% by volume hydrogen.
 6. Process as claimed in claim 1 wherein the total pressure during the reaction is at least 10 bar.
 7. Process as claimed in claim 6, wherein the total pressure is 40 to 200 bar.
 8. Process as claimed in claim 1, wherein the reaction temperature is in the range of 15° to 70° C.
 9. Process as claimed in claim 1, wherein the reaction medium contains up to 2 mol/l of a non-halogenated acid.
 10. Process as claimed in claim 9, wherein said acid is present in a concentration of about 0.001 mol/l to 0.5 mol/l.
 11. Process as claimed in claim 9, wherein the acid is phosphoric acid and/or sulphuric acid.
 12. Process as claimed in claim 1, wherein the reaction medium contains less than 0.5% by volume liquid organic components.
 13. Process as claimed in claim 1, wherein the catalyst is present in the form of a finely dispersed metal powder.
 14. Process as claimed in claim 1, wherein the catalyst is present bound to a solid supporting material.
 15. Process as claimed in claim 14, wherein the supporting material is selected from the group consisting of active charcoal, silicon carbide, zeolites, titanium dioxide, zirconium dioxide, aluminum oxide and materials based on silicic acid.
 16. Process as claimed in claim 15, wherein a supporting material of aluminium oxide is used.
 17. Process as claimed in claim 14 wherein the proportion of catalytically active metal is 0.1 to 10% by weight in relation to the total weight of metal and supporting material.
 18. Process as claimed in claim 14 wherein said catalyst has been produced by reducing said palladium halogenide and an iridium or rhodium, respectively, halogenide, in the set forth ratios to one another, in said aqueous solution in effective contact with a sufficient amount of a supporting material and said reducing agent comprising sodium formate under reducing conditions.
 19. Process as claimed in claim 14, wherein a palladium/gold alloy with a content of 9 to 95 atom % gold on a solid support is used.
 20. Process as claimed in claim 19, wherein the solid support is carbon.
 21. Process as claimed in claim 19, wherein said catalyst comprises a palladium/gold alloy, comprising 10 to 50 atom % gold, on an aluminium oxide support.
 22. Process as claimed in claim 21, wherein said catalyst is produced by mixing a hydrochloric acid solution of Pd chloride and Au chloride in the set forth ratio of Pd: Au with the set forth amount of aluminium oxide, heating said mixture at said non-hydrogen producing weekly acidic pH value, adding an excess of a reducing agent comprising sodium formate maintaining reducing condition, and removing chloride ions after the reduction.
 23. A process as claimed in claim 1 wherein said aqueous reaction mixture contains less than 0.5% by volume liquid organic components.
 24. A process as claimed in claim 1 wherein said aqueous reaction mixture is free of analyzable liquid organic components.
 25. Process for the production of hydrogen peroxide comprising:forming a substantially nitrogen free gas mixture comprising hydrogen and oxygen; forming a substantially chloride free aqueous reaction mixture containing: less than 2% by volume liquid organic components, and sodium bromide in an amount sufficient to provide at least about 0.000001 mol per liter bromide ions and at most 0.01 mol per liter halogen ions; and mixing a halogenide of palladium with a halogenide of gold to form a halogenide bimetal of palladium and 5 to 95 percent gold; reducing said mixture of a halogenide of palladium and a halogenide of gold with a non-hydrogen producing reducing agent consisting essentially of sodium formate to form a reduced bimetallic catalyst comprising palladium and 1 to 15 weight percent of gold; admixing said reduced bimetallic catalyst into said aqueous reaction mixture; passing said gas mixture through said aqueous reaction mixture; and contacting said gas mixture in said aqueous reaction mixture with said reduced bimetallic catalyst under conditions sufficient to convert hydrogen and oxygen in said gas mixture into hydrogen peroxide.
 26. Process as claimed in claim 25 wherein said bimetal catalyst is in the form of a finely dispersed powder, and wherein after said catalyst has been produced by a reduction of said palladium halogenide and a gold halogenide in an aqueous solution containing said sodium formate reducing agent;removing halogen ions produced by said reduction to produce a substantially halogen free metallic powder; and then combining said reduced, substantially halogen free metallic powder with said aqueous reaction mixture. 